CN114749743B - A high-temperature connection method for brazing C/C composite materials and Ni-based alloys using pure Cu - Google Patents

Abstract

The invention discloses a high-temperature connection method for soldering a C/C composite material and a Ni-based alloy by adopting pure Cu, which aims to solve the problem of poor high-temperature resistance of a solder used for soldering a joint of the C/C composite material and the Ni-based alloy. The high-temperature connection method comprises the following steps: 1. polishing the surface to be welded of the C/C composite material; 2. coating Sn-Cr metal paste on the surface to be welded of the pretreated C/C composite material, heating at 800-1050 ℃, and then placing the modified C/C composite material into a nitric acid solution to obtain a C/C composite material with the modified Cr-C coating surface; 3. and placing the Cu foil between the C/C composite material and the surface to be welded of the Ni-based alloy, and placing the Cu foil in a vacuum heating furnace for braze welding connection. According to the invention, pure Cu with high plasticity and excellent high temperature resistance is adopted as a brazing filler metal to realize the brazing of the C/C composite material and the Ni-based alloy, the obtained joint forms tight interface connection, and the joint has excellent room temperature and high temperature mechanical properties.

Description

A high-temperature connection method for brazing C/C composite materials and Ni-based alloys using pure Cu

technical field

The invention belongs to the field of connection of dissimilar materials, and in particular relates to a high-temperature connection method using pure Cu to braze C/C composite materials and Ni-based alloys.

Background technique

C/C composite material is an excellent carbon fiber reinforced carbon matrix composite material, which has low density (~1.8g/cm ³ ), low thermal expansion coefficient (~1.5×10 ^-6 K ^-1 ), high temperature resistance (>2000 ℃), high specific strength and specific modulus, high thermal conductivity and electrical conductivity, and excellent thermal shock resistance and corrosion resistance. Therefore, it has been increasingly widely used in industries such as aerospace, nuclear power and automobiles. However, the manufacturing process of C/C composites is complicated, the processing cost is high, and it is difficult to manufacture large-sized and complex-shaped structural parts, which greatly limits its practical application in engineering structures. This problem can be effectively solved by connecting it with a metal with good processing properties. Ni-based alloys are a class of high-temperature structural materials widely used in aerospace and nuclear energy fields due to their good processability, excellent high temperature resistance and corrosion resistance, creep resistance and high strength. Connecting C/C composite materials with Ni-based alloys can significantly reduce the structural weight and improve the working efficiency of the engine and other components. Structural materials are more widely used.

At present, brazing is an effective method to realize the connection of C/C composites and Ni-based alloys. However, there are many difficulties in the brazing connection of the two. Firstly, the C/C composite material is covalently bonded, its chemical properties are stable, and it is difficult to melt, and it is difficult for metals such as Ni to wet the surface of the C/C composite material. Secondly, the thermal expansion coefficient of C/C composite materials is low, and its value is about one-tenth of the thermal expansion coefficient of Ni-based alloys (~14×10 ^-6 K ^-1 ). Significant residual stresses develop in the joint. In particular, C/C composite materials are brittle materials, while Ni-based alloys often contain a large number of strengthening phases, and the plastic denaturation ability of the base metals on both sides is poor, so the residual stress in the joint is difficult to be released. As a result, the residual stresses in the joint will induce cracks at the interface, leading to failure of the joint. Therefore, it is very important to select the appropriate solder to relieve the residual stress of the joint. At present, researchers have developed brazing filler metals with high plasticity such as AgCuTi and AgTi, etc., to realize the connection of C/C composite materials and Ni-based alloys. However, these brazing filler metals have insufficient high temperature resistance, and their service temperature often does not exceed 500°C. At present, the commonly used high-temperature solders, such as NiTi, CuTi, CoTi and other solders, contain a large amount of brittle compounds resulting in poor plasticity, and it is difficult to achieve a reliable connection between C/C composites and Ni-based alloys. In addition, studies have also shown that commonly used high-temperature solders such as NiCrSiB are prone to cracks at the joint interface when brazing C/C composite materials and Ni-based alloys due to insufficient plasticity, reducing the reliability of the joint. Therefore, there is an urgent need to develop a new brazing method to achieve a reliable interface connection between the two and to make the joint have excellent high temperature resistance.

Contents of the invention

The purpose of the present invention is to solve the problems of poor high temperature resistance and low plasticity of the solder used in the brazing joints of C/C composite materials and Ni-based alloys at present, and provide a method of brazing C/C composite materials and Ni-based alloys using pure Cu. High temperature connection method.

The present invention adopts the high-temperature connection method of pure Cu brazing C/C composite material and Ni base alloy to realize according to the following steps:

Step 1. Use SiC sandpaper to polish the surface of the C/C composite material to be welded, and obtain the pretreated C/C composite material after cleaning and drying;

Step 2, preparing a Cr-C coating on the surface of the C/C composite material, the specific steps are as follows:

a. Carry out mechanical ball milling of 2.5-15% Cr powder and 97.5-85% Sn powder by mass percentage, mix uniformly to obtain Sn-Cr metal powder, then add binder and mix uniformly to obtain Sn-Cr metal paste ;

b. Coating the Sn-Cr metal paste on the surface of the pretreated C/C composite material to be welded, heating it in a vacuum heating furnace at a temperature of 800-1050°C, and obtaining a modified C/C composite material after cooling;

c. put the modified C/C composite material into the nitric acid solution to corrode and remove Sn, and obtain the C/C composite material with Cr-C coating surface modification after ultrasonic cleaning;

Step 3, brazing the C/C composite material with Cr-C coating surface modification and Ni-based alloy, the specific steps are as follows:

d. use SiC sandpaper to polish the surface to be welded of Ni-based alloy and Cu foil, and obtain Ni-based alloy and Cu foil after cleaning and drying;

e. Place the Cu foil between the Cr-C coating surface-modified C/C composite material and the Ni-based alloy surface to be welded to form a sandwich structure, put it in a vacuum heating furnace, and keep it warm at a temperature of 1100-1180 °C Make a brazed connection;

f. After the heat preservation is over, cool down and take out the weldment to complete the high-temperature brazing connection between the C/C composite material and the Ni-based alloy.

The high-temperature connection method of the present invention using pure Cu brazing C/C composite materials and Ni-based alloys mainly includes the following beneficial effects:

1. A uniform and dense Cr-C modified layer was prepared on the surface of the C/C composite material at a lower temperature by using the Sn-Cr alloy to react with the C/C composite material and combining the acid corrosion method, realizing the pure Cu in the original C The completely non-wetting state of the /C composite surface was transformed into good wetting on the Cr-C modified C/C composite surface;

2. Pure Cu with high plasticity and excellent high temperature resistance is used as the brazing material to realize the brazing of C/C composite materials and Ni-based alloys. The joints obtained form a tight interface connection, and the joints have excellent mechanical properties at room temperature and high temperature ;

3. In the obtained brazed joint, the brazing seam is mainly composed of Cu solid solution, no brittle compound is formed, the joint structure is simple, and the property is stable;

4. The ingredients used in the brazing material come from a wide range of sources, low cost, easy to operate, and convenient for industrial application.

Description of drawings

Fig. 1 is the optical photograph of the wetting state of pure Cu in the original C/C composite material (left figure) and the C/C composite material (right figure) through surface Cr-C modification in the embodiment;

Fig. 2 adopts the scanning electron micrograph of the microscopic joint of pure Cu brazing surface modification C/C composite material and Ni-based single crystal alloy DD3 joint in the embodiment;

Fig. 3 adopts the scanning electron micrograph of C/C interface microstructure in the joint of pure Cu brazing surface modification C/C composite material and Ni base single crystal alloy DD3 in the embodiment;

Fig. 4 is a scanning electron micrograph of the DD3 interface microstructure in the joint between the surface-modified C/C composite material and the Ni-based single crystal alloy DD3 brazed with pure Cu in the example.

Detailed ways

Specific implementation mode 1: This implementation mode adopts the high-temperature connection method of pure Cu brazing C/C composite material and Ni-based alloy according to the following steps:

Step 1. Use SiC sandpaper to polish the surface of the C/C composite material to be welded, and obtain the pretreated C/C composite material after cleaning and drying;

Step 2, preparing a Cr-C coating on the surface of the C/C composite material, the specific steps are as follows:

a. Carry out mechanical ball milling of 2.5-15% Cr powder and 97.5-85% Sn powder by mass percentage, mix uniformly to obtain Sn-Cr metal powder, then add binder and mix uniformly to obtain Sn-Cr metal paste ;

b. Coating the Sn-Cr metal paste on the surface of the pretreated C/C composite material to be welded, heating it in a vacuum heating furnace at a temperature of 800-1050°C, and obtaining a modified C/C composite material after cooling;

c. put the modified C/C composite material into the nitric acid solution to corrode and remove Sn, and obtain the C/C composite material with Cr-C coating surface modification after ultrasonic cleaning;

Step 3, brazing the C/C composite material with Cr-C coating surface modification and Ni-based alloy, the specific steps are as follows:

d. use SiC sandpaper to polish the surface to be welded of Ni-based alloy and Cu foil, and obtain Ni-based alloy and Cu foil after cleaning and drying;

e. Place the Cu foil between the Cr-C coating surface-modified C/C composite material and the Ni-based alloy surface to be welded to form a sandwich structure, put it in a vacuum heating furnace, and keep it warm at a temperature of 1100-1180 °C Make a brazed connection;

f. After the heat preservation is over, cool down and take out the weldment to complete the high-temperature brazing connection between the C/C composite material and the Ni-based alloy.

In this embodiment, the surface of the C/C composite material is modified first, and then pure Cu with high plasticity and excellent high temperature resistance is used as the solder to braze the two. The joint can form a reliable interface connection and obtain excellent high temperature resistance. mechanical properties.

Embodiment 2: This embodiment is different from Embodiment 1 in that the binder described in step a is an aqueous solution of carboxymethyl cellulose.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the heat treatment time in step b is 10-60 min.

Embodiment 4: This embodiment differs from Embodiments 1 to 3 in that the volume fraction of the nitric acid solution in step c is 10% to 30%.

Embodiment 5: This embodiment differs from Embodiments 1 to 4 in that the thickness of the Cu foil in step d is 0.05-0.5 mm.

Embodiment 6: This embodiment differs from Embodiments 1 to 5 in that the Ni-based alloy in step d is a single crystal Ni-based superalloy, GH superalloy, Inconel alloy or Monel alloy.

Embodiment 7: This embodiment differs from Embodiment 1 to Embodiment 6 in that the vacuum degree in the vacuum heating furnace in step e is lower than 3×10 ⁻³ Pa.

Embodiment 8: This embodiment differs from Embodiments 1 to 7 in that in step e, the heating rate is controlled to be 5-15° C./min to raise the temperature to the brazing temperature.

Embodiment 9: This embodiment differs from Embodiment 8 in that the heat preservation time of the brazing connection in step e is 10-60 minutes.

Embodiment 10: This embodiment differs from Embodiments 1 to 9 in that the cooling in step f is to cool the weldment to 380-420°C at a cooling rate of 5°C/min, and then cool to room temperature with the furnace.

Embodiment: This embodiment adopts the high-temperature connection method of pure Cu brazing C/C composite material and Ni-based alloy according to the following steps:

Step 1. Use 1200# SiC sandpaper to polish the surface of the C/C composite material to be welded, put it into absolute ethanol and ultrasonically clean it for 3 times, each time for 5 minutes, and dry it to obtain the pretreated C/C composite material;

Step 2, preparing a Cr-C coating on the surface of the C/C composite material, the specific steps are as follows:

a. Carry out mechanical ball milling of 10% Cr powder and 90% Sn powder by mass percentage, mix uniformly to obtain Sn-Cr metal powder, then add binder and mix uniformly to obtain Sn-Cr metal paste;

b. Coating the Sn-Cr metal paste on the surface of the pretreated C/C composite material to be welded, heating in a vacuum heating furnace at a temperature of 800 ° C for 30 minutes, and obtaining a modified C/C composite material after cooling;

c. put the modified C/C composite material into the nitric acid (water) solution with a volume fraction of 30% and corrode it for 60min, remove Sn, put it into absolute ethanol for ultrasonic cleaning, and obtain Cr-C coating surface modified C/C composite material;

Step 3, brazing the C/C composite material with Cr-C coating surface modification and Ni-based alloy, the specific steps are as follows:

d. Use 400#, 800#, 1200# SiC sandpaper to polish the Ni-based alloy surface to be welded, use 1200# SiC sandpaper to polish both sides of the Cu foil, and put the polished Ni-based alloy and Cu foil into absolute ethanol for ultrasonic Wash 3 times, each time for 5 minutes, and dry to obtain the cleaned Ni-based alloy and Cu foil;

e. Place the Cu foil between the Cr-C coating surface-modified C/C composite material and the Ni-based alloy surface to be welded to form a sandwich structure, and put it into a vacuum heating furnace with a vacuum degree lower than 3×10 ⁻ At ³ Pa, turn on the heating switch, control the heating rate from 15°C/min to 450°C, 10°C/min to 800°C, 5°C/min to 1140°C, keep warm for 30 minutes for brazing connection;

f. After the heat preservation is over, the weldment is cooled to about 400°C at a cooling rate of 5°C/min, and then cooled to room temperature with the furnace, and the test piece is taken out to complete the high-temperature brazing connection of the C/C composite material and the Ni-based alloy.

In this example, under the conditions of 1140° C. and heat preservation for 30 minutes, a C/C composite material of 10 mm×10 mm×3 mm and a DD3 alloy of 5 mm×5 mm×3 mm were brazed using pure Cu foil. The test results show that the shear strength of the brazed joint between C/C composite material and Ni-based alloy can reach 30.3MPa at room temperature and 22.8MPa at 800℃.

Figure 1 is an optical photograph of the wetting state of pure Cu on the original C/C composite and the surface Cr-C modified C/C composite. It can be seen that pure Cu is not wet on the surface of the original C/C composite , and formed a good wetting and spreading on the C/C surface modified by Cr-C surface.

Figure 2 is a scanning electron microscope photo of the microscopic joint between the surface-modified C/C composite material and the Ni-based single crystal alloy DD3 joint brazed with pure Cu. It can be seen that the joint forms a tight connection, and the brazing seam is mainly composed of Cu solid solution. No brittle compounds were formed.

Figure 3 is a scanning electron micrograph of the microstructure of the C/C interface in the joint between the surface-modified C/C composite material and the Ni-based single crystal alloy DD3 brazed with pure Cu. It can be seen that the interface between the solder and the C/C composite material is well connected , the interface has no defects such as cracks and holes.

Figure 4 is a scanning electron micrograph of the microstructure of the DD3 interface between the surface-modified C/C composite material and the Ni-based single crystal alloy DD3 joint using pure Cu brazing. It can be seen that the interface between the solder and the DD3 alloy is well connected, forming a layer Clear solid solution and diffusion layers.

Claims (10)

1. The high-temperature connection method for soldering the C/C composite material and the Ni-based alloy by adopting pure Cu is characterized in that the high-temperature connection method for soldering the C/C composite material and the Ni-based alloy is realized according to the following steps:

polishing the surface to be welded of the C/C composite material by adopting SiC abrasive paper, and cleaning and drying to obtain a pretreated C/C composite material;

preparing a Cr-C coating on the surface of the C/C composite material, wherein the specific steps are as follows:

a. mechanically ball milling Cr powder with the mass percentage of 2.5-15% and Sn powder with the mass percentage of 97.5-85%, uniformly mixing to obtain Sn-Cr metal powder, and then adding a binder and uniformly mixing to obtain Sn-Cr metal paste;

b. coating Sn-Cr metal paste on the surface to be welded of the pretreated C/C composite material, heating the surface to be welded in a vacuum heating furnace at 800-1050 ℃, and cooling the surface to obtain a modified C/C composite material;

c. putting the modified C/C composite material into a nitric acid solution to remove Sn by corrosion, and performing ultrasonic cleaning to obtain a Cr-C coating surface modified C/C composite material;

step three, brazing the C/C composite material with the modified Cr-C coating surface and the Ni-based alloy, wherein the specific steps are as follows:

d. polishing the surfaces to be welded of the Ni-based alloy and the Cu foil by adopting SiC abrasive paper, and cleaning and drying to obtain the cleaned Ni-based alloy and Cu foil;

e. placing Cu foil between the C/C composite material modified on the surface of the Cr-C coating and the surface to be welded of the Ni-based alloy, placing the Cu foil in a vacuum heating furnace, and carrying out brazing connection at the temperature of 1100-1180 ℃;

f. and after the heat preservation is finished, cooling, taking out the weldment, and completing the high-temperature brazing connection of the C/C composite material and the Ni-based alloy.

2. The method for high temperature joining of a pure Cu braze C/C composite to a Ni-based alloy according to claim 1, characterized in that the binder in step a is an aqueous carboxymethyl cellulose solution.

3. The high temperature joining method using pure Cu brazing C/C composite material and Ni-based alloy according to claim 1, characterized in that the heating treatment time in step b is 10 to 60min.

4. The high temperature joining method using pure Cu brazing C/C composite material with Ni-based alloy according to claim 1, characterized in that the volume fraction of the nitric acid solution in step C is 10% to 30%.

5. The high temperature joining method using pure Cu brazing C/C composite material with Ni-based alloy as claimed in claim 1, characterized in that the Cu foil in step d has a thickness of 0.05-0.5 mm.

6. The high temperature joining method using pure Cu brazing C/C composite material with Ni-based alloy according to claim 1, characterized in that in step d the Ni-based alloy is a single crystal Ni-based superalloy, a GH superalloy, an Inconel alloy or a Monel alloy.

7. The high temperature joining method using pure Cu brazing C/C composite material and Ni-based alloy according to claim 1, wherein the vacuum degree in the vacuum heating furnace in step e is lower than 3X 10 ^-3 Pa。

8. The high temperature connection method using pure Cu brazing C/C composite material and Ni-based alloy according to claim 1, characterized in that in step e the temperature rising rate is controlled to be 5-15 ℃/min to rise to the brazing temperature.

9. The high temperature joining method using pure Cu brazing C/C composite material and Ni-based alloy according to claim 8, characterized in that the heat preservation time of the brazing joining in step e is 10-60 min.

10. The high temperature joining method using pure Cu brazing C/C composite material and Ni-based alloy according to claim 1, characterized in that the cooling in step f is cooling the weldment to 380-420 ℃ at a cooling rate of 5 ℃/min, followed by furnace cooling to room temperature.

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